1. Group Health Research Institute, Seattle, Washington.
2. Department of Epidemiology, University of Washington, Seattle, Washington.
3. Department of Obstetrics and Gynecology, University of Washington School of Medicine, Seattle, Washington.
4. Fred Hutchinson Cancer Research Institute, Seattle, Washington.
5. Department of Population Medicine, Harvard Medical School/Harvard Pilgrim Health Care Institute; Department of Medicine, Harvard Vanguard Medical Associates, Boston, Massachusetts.